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Subject[PATCH] x86/asm/entry/32: Update ENOSYS handling to match 64-bit logic
Date
Sometime ago Andy changed 64-bit syscall logic so that pt_regs->ax is
initially set to -ENOSYS, and on exit from syscall, it is updated with
actual return value. This simplified logic there.

This patch does the same for 32-bit syscall entry points.

The check for %rax being too big is moved to be just before
the call insn which dispatches execution through syscall table.
There is no way to accidentally skip this check now by jumping
to a label after it. This allows to remove redundant checks
after e.g. ptrace.

If %rax is too big, we just skip over the (call, write %rax to pt_regs->ax)
insn pair. pt_regs->ax remains set to -ENOSYS, and it gets returned
to userspace.

Similar to 64-bit code, this eliminates "ia32_badsys" code path.

Run-tested.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: Will Drewry <wad@chromium.org>
CC: Kees Cook <keescook@chromium.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---
arch/x86/ia32/ia32entry.S | 44 +++++++++++++++-----------------------------
1 file changed, 15 insertions(+), 29 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index a821b1c..29ab1c2 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -142,7 +142,7 @@ ENTRY(ia32_sysenter_target)
pushq_cfi_reg rsi /* pt_regs->si */
pushq_cfi_reg rdx /* pt_regs->dx */
pushq_cfi_reg rcx /* pt_regs->cx */
- pushq_cfi_reg rax /* pt_regs->ax */
+ pushq_cfi $-ENOSYS /* pt_regs->ax */
cld
sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
CFI_ADJUST_CFA_OFFSET 10*8
@@ -169,8 +169,6 @@ sysenter_flags_fixed:
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
CFI_REMEMBER_STATE
jnz sysenter_tracesys
- cmpq $(IA32_NR_syscalls-1),%rax
- ja ia32_badsys
sysenter_do_call:
/* 32bit syscall -> 64bit C ABI argument conversion */
movl %edi,%r8d /* arg5 */
@@ -179,8 +177,11 @@ sysenter_do_call:
movl %ebx,%edi /* arg1 */
movl %edx,%edx /* arg3 (zero extension) */
sysenter_dispatch:
+ cmpq $(IA32_NR_syscalls-1),%rax
+ ja 1f
call *ia32_sys_call_table(,%rax,8)
movq %rax,RAX(%rsp)
+1:
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF
testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -247,9 +248,7 @@ sysexit_from_sys_call:
movl %ebx,%esi /* 2nd arg: 1st syscall arg */
movl %eax,%edi /* 1st arg: syscall number */
call __audit_syscall_entry
- movl RAX(%rsp),%eax /* reload syscall number */
- cmpq $(IA32_NR_syscalls-1),%rax
- ja ia32_badsys
+ movl ORIG_RAX(%rsp),%eax /* reload syscall number */
movl %ebx,%edi /* reload 1st syscall arg */
movl RCX(%rsp),%esi /* reload 2nd syscall arg */
movl RDX(%rsp),%edx /* reload 3rd syscall arg */
@@ -269,7 +268,7 @@ sysexit_from_sys_call:
1: setbe %al /* 1 if error, 0 if not */
movzbl %al,%edi /* zero-extend that into %edi */
call __audit_syscall_exit
- movq RAX(%rsp),%rax /* reload syscall return value */
+ movq ORIG_RAX(%rsp),%rax /* reload syscall return value */
movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),%edi
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF
@@ -300,13 +299,10 @@ sysenter_tracesys:
#endif
SAVE_EXTRA_REGS
CLEAR_RREGS
- movq $-ENOSYS,RAX(%rsp)/* ptrace can change this for a bad syscall */
movq %rsp,%rdi /* &pt_regs -> arg1 */
call syscall_trace_enter
LOAD_ARGS32 /* reload args from stack in case ptrace changed it */
RESTORE_EXTRA_REGS
- cmpq $(IA32_NR_syscalls-1),%rax
- ja int_ret_from_sys_call /* sysenter_tracesys has set RAX(%rsp) */
jmp sysenter_do_call
CFI_ENDPROC
ENDPROC(ia32_sysenter_target)
@@ -376,7 +372,7 @@ ENTRY(ia32_cstar_target)
pushq_cfi_reg rdx /* pt_regs->dx */
pushq_cfi_reg rbp /* pt_regs->cx */
movl %ebp,%ecx
- pushq_cfi_reg rax /* pt_regs->ax */
+ pushq_cfi $-ENOSYS /* pt_regs->ax */
sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
CFI_ADJUST_CFA_OFFSET 10*8

@@ -392,8 +388,6 @@ ENTRY(ia32_cstar_target)
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
CFI_REMEMBER_STATE
jnz cstar_tracesys
- cmpq $IA32_NR_syscalls-1,%rax
- ja ia32_badsys
cstar_do_call:
/* 32bit syscall -> 64bit C ABI argument conversion */
movl %edi,%r8d /* arg5 */
@@ -402,8 +396,11 @@ cstar_do_call:
movl %ebx,%edi /* arg1 */
movl %edx,%edx /* arg3 (zero extension) */
cstar_dispatch:
+ cmpq $(IA32_NR_syscalls-1),%rax
+ ja 1f
call *ia32_sys_call_table(,%rax,8)
movq %rax,RAX(%rsp)
+1:
DISABLE_INTERRUPTS(CLBR_NONE)
TRACE_IRQS_OFF
testl $_TIF_ALLWORK_MASK, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
@@ -450,14 +447,11 @@ cstar_tracesys:
xchgl %r9d,%ebp
SAVE_EXTRA_REGS
CLEAR_RREGS r9
- movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
movq %rsp,%rdi /* &pt_regs -> arg1 */
call syscall_trace_enter
LOAD_ARGS32 1 /* reload args from stack in case ptrace changed it */
RESTORE_EXTRA_REGS
xchgl %ebp,%r9d
- cmpq $(IA32_NR_syscalls-1),%rax
- ja int_ret_from_sys_call /* cstar_tracesys has set RAX(%rsp) */
jmp cstar_do_call
END(ia32_cstar_target)

@@ -516,7 +510,7 @@ ENTRY(ia32_syscall)
pushq_cfi_reg rsi /* pt_regs->si */
pushq_cfi_reg rdx /* pt_regs->dx */
pushq_cfi_reg rcx /* pt_regs->cx */
- pushq_cfi_reg rax /* pt_regs->ax */
+ pushq_cfi $-ENOSYS /* pt_regs->ax */
cld
sub $(10*8),%rsp /* pt_regs->r8-11,bp,bx,r12-15 not saved */
CFI_ADJUST_CFA_OFFSET 10*8
@@ -524,8 +518,6 @@ ENTRY(ia32_syscall)
orl $TS_COMPAT, ASM_THREAD_INFO(TI_status, %rsp, SIZEOF_PTREGS)
testl $_TIF_WORK_SYSCALL_ENTRY, ASM_THREAD_INFO(TI_flags, %rsp, SIZEOF_PTREGS)
jnz ia32_tracesys
- cmpq $(IA32_NR_syscalls-1),%rax
- ja ia32_badsys
ia32_do_call:
/* 32bit syscall -> 64bit C ABI argument conversion */
movl %edi,%r8d /* arg5 */
@@ -533,9 +525,12 @@ ia32_do_call:
xchg %ecx,%esi /* rsi:arg2, rcx:arg4 */
movl %ebx,%edi /* arg1 */
movl %edx,%edx /* arg3 (zero extension) */
+ cmpq $(IA32_NR_syscalls-1),%rax
+ ja 1f
call *ia32_sys_call_table(,%rax,8) # xxx: rip relative
ia32_sysret:
movq %rax,RAX(%rsp)
+1:
ia32_ret_from_sys_call:
CLEAR_RREGS
jmp int_ret_from_sys_call
@@ -543,23 +538,14 @@ ia32_ret_from_sys_call:
ia32_tracesys:
SAVE_EXTRA_REGS
CLEAR_RREGS
- movq $-ENOSYS,RAX(%rsp) /* ptrace can change this for a bad syscall */
movq %rsp,%rdi /* &pt_regs -> arg1 */
call syscall_trace_enter
LOAD_ARGS32 /* reload args from stack in case ptrace changed it */
RESTORE_EXTRA_REGS
- cmpq $(IA32_NR_syscalls-1),%rax
- ja int_ret_from_sys_call /* ia32_tracesys has set RAX(%rsp) */
jmp ia32_do_call
+ CFI_ENDPROC
END(ia32_syscall)

-ia32_badsys:
- movq $0,ORIG_RAX(%rsp)
- movq $-ENOSYS,%rax
- jmp ia32_sysret
-
- CFI_ENDPROC
-
.macro PTREGSCALL label, func
ALIGN
GLOBAL(\label)
--
1.8.1.4


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